When the dispersion analysis of an aerosol is carried out photoelectrically, it is important to determine the size of each particle. The amplitude of electric pulses at the output of the photoelectric converter is proportional to particle sizes and also depends upon the sensitivity of the converter, which varies following changes in the voltage applied to the lamp and photosensitive element, the ambient temperature and other factors.
Variations in the sensitivity of the photoelectric converter lead to changes in the electric pulse amplitudes, which, in turn, accounts for errors in the determination of particle sizes.
In order to increase the accuracy of the dispersion analysis, it is necessary to calibrate the sensitivity of the photoelectric converter.
There is known a photoelectric converter of sizes of particles contained in a flow of gas to electric pulses (cf. "The Photoelectric Particle Counter of the A3-5 Type", SHF Electronics, 1970, Series 10, p. 92 in Russian), comprising a chamber with a means for directing an aerosol flow into and from the chamber which is optically connected to an illumination means forming a convergent light flux to illuminate the aerosol flow, and to a photoreceiver.
The illumination means and the photoreceiver are arranged so that their optical axes and the axis of the aerosol flow all intersect at a right angle inside the chamber. The photoelectric converter under review further includes a channel to transmit part of the light flux generated by the illumination means to the photoreceiver. The latter is a light guide arranged outside the chamber and optically connected thereto. Finally, the photoelectric converter includes a calibration light pulse former comprising a diaphragm installed at the input of the light guide, and a mechanical shutter constructed as a slotted disc. The mechanical shutter is coupled to a rotation drive. The shutter and light guide are accommodated in a common housing.
The channel for transmitting part of the light flux to the photoreceiver is of a complex configuration and great length, whereby it lacks rigidity. This disadvantage accounts for an unstable amplitude of calibration light pulses.
Besides, the use of the rotation drive makes it hard to synchronize the calibration light pulses with electric control pulses produced by the electronic means incorporated in the device for the dispersion analysis of aerosols.